Changes in plastics manufacturing strategies, particularly the growing emphasis on reducing in-process time and inventories, make multishot molding more viable and cost justifiable than single shot molding for a broader range of manufacturers. The multishot process allows multiple colors or materials to be sequentially injected in a single, continuous process to speed throughput, minimize production and assembly operations, improve part quality. and create innovative part features.
In most cases, a single injection molding machine with multiple injection units will cost less than separate machines with an equivalent number of single injection units. Likewise, a single two-color mold will usually cost less than two one-color molds. There is also a labor savings when using a multishot machine because only a single machine operator is required for the multi-step process. This can have major impact on payback calculations and life cycle costs. Floor space, electricity, and other utility costs are also reduced by consolidating operations on one machine. Faster inventory turns for savings on in-process inventory can be a critical factor in the decision matrix as well.
Despite their advantages, multishot injection molding machines are not readily available from the inventory of large press manufacturers and must often be custom built which results in several months of delay before the desired production can commence. Once the multishot machine is delivered and installed, the customer is locked into the particular arrangement of the multiple injection units on the machine. There is no interchangeability with another press manufacturer's machine or parts thereof.
Accordingly, it is desirable to provide an arrangement for removably mounting an injection molding unit on a commercially available injection molding machine in a manner which will produce all the advantages of a multishot machine without any of its drawbacks. It is also desirable to provide a flexible framework for retrofitting additional injectors onto standard injection molding machines.